Polarization-Independent Photon Storage System with Variable Time Delay*

Quantum optical memories are a key component for a variety of quantum information applications, from extending quantum communication channels to building high-efficiency single-photon sources. However, current broad bandwidth photon storage systems we've seen operate at somewhat low efficiency and short storage times (on the order of 10 ns). Here we develop a system with multiplexed free-space storage cavities, able to store single photons with high efficiency over variable delays [N x 12.5 ns, 1 $\le $ N $\le $ 999], and over several nanometers bandwidth. The system can store multiple photons simultaneously and can potentially store qubits encoded in various degree of freedoms (e.g., polarization, timing, and spatial modes). We have demonstrated a process fidelity \textgreater 98{\%} for storage times up to 125 ns and \textgreater 90{\%} for up to 500 ns. A future goal for this experiment is to achieve storage of hyperentanglement. While previous hyperentangled photon storage systems only achieved 5{\%} efficiency, we have currently demonstrated fiber-coupled transmission above 65{\%} for delay times up to 125 ns, and free-space transmission above 50{\%} for delay times up to 5 $\mu $s.